1. Field of the Invention
The present invention relates to hybrid electric vehicles having a primary power source and an electric energy storage system.
2. Background Art
There are a number configurations of hybrid electric vehicles (HEVs). Some HEVs include a primary power source (PPS) and an electric energy storage system (ESS). Both power sources can provide electric power for powering a motor.
The motor converts electric power to mechanical power for driving the vehicle. The motor can be the only source of mechanical power for driving the vehicle and/or the motor can operate in conjunction with an engine or other drive means.
The PPS can be a fuel cell, a combined engine-generator, or other electric power producing means. The ESS can be a battery, a capacitor, a combination of the two, or some other device capable of storing and discharging electric energy.
U.S. Pat. No. 5,820,172, which is owned by the assignee of this application, discloses a powertrain for a hybrid electric vehicle wherein the PPS and the ESS are controlled to meet a motive power demand by determining the most fuel efficient combination of PPS and ESS power output.
An imbalance of power generation and power consumption requires frequent charging and discharging of the ESS, thus reducing ESS life and reducing total system efficiency.
A controller disclosed in the '172 patent incurs substantial processing time as it must compute all possible combinations of PPS and ESS power outputs that satisfy the motive power demand. It is desirable, therefore, to provide an improved method with minimal processing time for determining a fuel efficient combination of PPS and ESS power output.